I am not sure yet, I was thinking of dark blue
korg mono/poly 
ARP 2600 http://www.vintagesynth.com/arp/arp2600blue.jpg 
but I love as well darker warm tones as with LinnDrum, but I’m not sure it would look good with the metal.
I don’t remember ever seing a piece of green hardware, so maybe that could be an option as well… hmm.